Germ free rats were immunized orally, intragastrically and intramucosally with Streptococcus mutans 6715-15. Unimmunized animals served as controls. All rats were infected with S. mutans 6715-15. After 8 weeks the rats were sacrificed and serum, saliva, gut and pulmonary washes were collected. In addition, splenic, salivary, mesenteric and Peyer's Patch lymphocytes were assayed. Serum and salivary antibodies were detected in all groups. Primed lymphocytes were detected in spleen and salivary lymph nodes.